Gray-scale digital images include pixels that are black, white, and various shades of gray. Bitonal digital images include only pixels that are either black or white. A gray-scale digital image can be converted to a bitonal image using a process known as thresholding. Thresholding gray-scale images to produce bitonal images can be useful, for example, in separating foreground features of a check, such as handwriting and printed text, from background features of a check, such as background patterns, in order to make the foreground features of the check more readable for humans or optical character recognition (OCR) techniques.
Typical thresholding techniques generally convert each pixel of a gray-scale image to a black pixel if the intensity of the gray-scale pixel is above a threshold and convert the pixel to a white pixel otherwise. However, typical thresholding techniques may not be effective for some check images. In particular, foreground intensity levels in some check images may not differ significantly from background intensity levels due to noise or widely varying intensities in the background and/or foreground. Thus, typical thresholding techniques may produce an image of a check that does not accurately depict foreground features of the check.